Screw fastener



F. K. KNOHL Sept. 21, 1965 United States Patent Ofi 3,207,023 PatentedSept. 21, 1965 ice 4 Claims. (Cl. 85-46) This application is acontinuation of my copending application, Serial No. 156,377 filedDecember 1, 1961, which is now abandoned.

The present invention relates to a novel fastener structure, and morespecifically to a novel rotary fastener device such as a screw or thelike.

An important object of the present invention is to provide a novel screwmember capable of forming complementary thread means in a workpieceduring application to the workpiece, which screw member is constructedso as to provide improved holding power and resistance to looseningwhile reducing any possibility of stripping or shearing of thecomplementary thread means formed in the workpiece.

A further important object of the present invention is to provide anovel screw member of the above described type and adapted selectivelyto be used for application to wood or similar materials or forapplication to sheet metal and the like.

A further object of the present invention is to provide a novel screwmember of the above described type which may be relatively easilystarted and driven into a workpiece without requiring pre-drilling andwithout damage to the screw member or the workpiece.

Other objects and advantages of the present invention will becomeapparent from the following description and the accompanying drawingwherein:

FIG. 1 is a partial sectional view showing a screw member incorporatingfeatures of the present invention driven into a workpiece;

FIG. 2 is an enlarged fragmentary sectional view showing a portion ofthe screw member in greater detail;,

FIG. 3 is an entering end view of the screw member shown in FIGS. 1 and2;

FIG. 4 is a fragmentary sectional view similar to FIG. 2 but showing amodified form of the present invention; and

FIG. 5 is an entering end view of the screw member shown in FIG. 4.

Referring now more specifically to the drawings wherein like parts aredesignated by the same numerals throughout the various figures, a screwmember 10 incorporating one embodiment of the present invention is shownin FIGS. 1, 2 and 3. While it will be apparent that the screw member maybe used for various purposes, FIG. 1 shows an installation wherein thescrew member 10 is used to secure a plate 12 to a wooden support member14.

The screw member 10 comprises an elongated shank 16 of substantiallyuniform diameter throughout its length. A tapered or substantiallypointed section 18 is provided at the entering end of the shank, and anenlarged head section 20 is integrally joined with the trailing end ofthe shank. A slot 22 or other suitable tool engageablemeans is providedin the head section 20.

In accordance with a feature of the present invention, the screw memberis provided with a first helical thread 24 integral with the shank 16and having a plurality of convolutions extending along the shank. Asecond helical thread 26 is provided on the shank and includes aplurality of convolutions spaced along the shank between theconvolutions of the thread 24. The threads 24 and 26 have substantiallythe same pitch. However, it is to be noted that the thread 24 has arelatively great heighth and a small included angle as compared with thethread 26. In the embodiment shown the height of the thread 24 isapproximately twice that of the thread 26. The included angle of thethread 24 is preferably approximately thirty degrees while the includedangle of the thread 26 is about forty-five degrees.

When the screw member 10 is applied to a workpiece such as the woodensupport 14, the threads 24 and 26 will form complementary thread meansin the workpiece. The relatively high thread 24 will project or biteinto the workpiece relatively deeply for increasing the area ofengagement between the thread and the workpiece. The aforementionedrelatively small included angle of the thread 24 which provides thethread with a narrow profile as shown best in FIG. 2, facilitates easyentry of the thread into the workpiece without injury to the screwmember and without splitting or otherwise damaging the workpiece. Therelatively short thread 26 also projects into the workpiece and adds tothe area of thread engagement with the workpiece and therefore increasesthe holding power and resistance to loosening of the screw member.However, it is to be noted that since the crests of the convolutions ofthe thread 24 project well beyond the thread 26, the length of theeffective shear line provided by the screw member 10 is determined bythe thread 24 and coincides with the pitch of the thread 24. The lengthof this effective shear line or pitch of the thread 24 is about twicethe distance between adjacent convolutions of the threads 24 and 26.Thus, while the thread convolutions 26 provides the device withincreased holding power and resistance to loosening, it does not reducethe length of the effective shear line so that when the screw member isapplied to the work structure as shown in FIG. 1, and possibility ofstripping or shearing the complementary thread means formed in theworkpiece 14 is minimized.

Since the included angle of the thread 26 is larger than the includedangle of the thread 24, the root of the thread 26 is similar inthickness to that of the thread 24. In other words, the roots of all ofthe thread convolutions are similar in thickness and are substantiallyequally spaced along the shank. This arrangement enables the screwmember to be applied to a sheet metal work structure, not shown, as wellas to a wooden work structure. In other words, the screw member 10 maybe selectively used as a wood screw or as a sheet metal fastener.

The entering end section 18 of the screw member 10 is preferably formedso as to be capable of drilling an aperture in a work structure duringapplication of the screw member to the work structure. In thisembodiment, the section 18 is substantially pointed and is formed with aplurality of substantially identical sides 28, 30, 32 and 34 whichintersect each other along converging and intersecting corners or lines36, 38, 40 and 42. The corners 36-42 provide cutting edges for enablingthe entering end section 18 of the screw member to drill or ream anaperture in a work structure. Preferably, the side surfaces 28-34 of thepointed end section are provided with a concave configuration as shownbest in FIG. 3, so as to relieve the entering end section 18 behind thecutting edges and thereby promote a more efiicient cutting action.

FIGS. 4 and 5 show a device which is similar to the structure describedabove as indicated by the application of identical reference numeralswith the suffix a to corresponding elements. This embodiment diiiers inthat a third thread 44 is provided on the shank 16a which thread has aplurality of helical convolutions spaced along the shank between theconvolutions of the threads 24a and 26a. The thread 44 is identical tothe thread 2601. The thread convolutions of this embodiment are, likethe structure described above, substantially uniformly spaced along theshank 16a so that the structure may be selective ly applied to wood andsimilar materials or sheets of metal and the like. The additional threadprovides for increased engagement with the work structure and greaterholding power.

The screw member a also includes a modified entering end section ordrill point 18a. In this embodiment two of the side portions 30a and 32aare relieved substantial amounts so as to provide faces 46 and 48substantially in a plane containing the longitudinal axis of the screwmember and intersecting the side surfaces 28a and 34a at acute anglesfor promoting a more effective cutting action at the corners or edges36a and 40a.

While the preferred embodiments of the present invention have been shownand described herein, it is obvious that many structural details may bechanged without departing from the spirit and scope of the appendedclaims.

The invention is claimed as follows:

1. A screw member for drilling .into a non-metallic workpiece comprisingan axially extending shank including an elongated portion having asubstantially uniform predetermined diameter throughout its length, afirst long lead helical thread having a plurality of convolutions onsaid shank and a relatively large predetermined height and being ofsubstantially uniform size and shape throughout, a second long leadhelical thread having a plurality of convolutions and a heightsubstantially less than said predetermined height and substantiallygreater than said predetermined diameter and. being of substantiallyuniform size and shape throughout, both of said threads having crestspresenting sharp edges for facilitating penetration of a workpiece, saidfirst thread having a relatively small included angle and said secondthread having an included angle substantially larger than said firstthread, all of said threads having roots of substantially the same axialextent, and said shank including a substantially pointed work drillingtip, all of said threads having a substantially uniform root diameterthroughout and subsequently terminating short of said tip, said tipcomprising a cutting edge extending substantially to said diameter ofsaid elongated shank portion for drilling a hole in a workpiece having adiameter substantially the same as said shank portion, said tip beingrecessed adjacent said cutting edge for promoting faster cutting actionand providing a cavity for accommodating material cut from theworkpiece, said cutting edge and recess extending substantially to andterminating at said threads for drilling a hole having a diameter equalto said root diameter prior to engagement of the threads with theworkpieces.

2. A screw member, as defined in claim 1, which includes a third helicalthread having a plurality of convolutions on said shank betweentheconvolutions of said first and second threads, said third thread havinga height substantially less than said predetermined height.

3. A screw member, as defined in claim 1 wherein said first thread hasan included angle of about thirty degrees and said second thread has anincluded angle of about forty-five degrees.

4. A screw member, as defined in claim 1, wherein said roots are spacedfrom each other substantially equal distances at least as greatas theaxial extent of said roots.

References Cited by the Examiner UNITED STATES PATENTS 410,698 9/89Rogers 48 2,956,470 10/60 Knohl 85-47 FOREIGN PATENTS 251,409 5/26 GreatBritain. 50,995 1/10- Switzerland.

CARL W. TOMLIN, Primary Examiner.

EDWARD C. ALLEN, Examiner.

1. A SCREW MEMBER FOR DRILLING INTO A NON-METALLIC WORKPIECE COMPRISINGAN AXIALLY EXTENDING SHANK INCLUDING AN ELONGATED PORTION HAVING ASUBSTANTIALLY UNIFORM PREDETERMINED DIAMETER THROUGHOUT ITS LENGTH, AFIRST LONG LEAD HELICAL THREAD HAVING A PLURALITY OF CONVOLUTIONS ONSAID SHANK AND A RELATIVELY LARGE PREDETERMINED HEIGHT AND BEING OFSUBSTANTIALLY UNIFORM SIZE AND SHAPE THROUGHOUT, A SECOND LONG LEADHELICAL THREAD HAVING A PLURALITY OF CONVOLUTIONS AND A HEIGHTSUBSTANTIALLY LESS THAN SAID PREDETERMINED HEIGHT AND SUBSTANTIALLYGREATER THAN SAID PREDETERMINED DIAMETER AND BEING OF SUBSTANTIALLYUNIFORM SIZE AND SHAPE THROUGHOUT, BOTH OF SAID THREADS HAVING CRESTSPRESENTING SHARP EDGES FOR FACILITATING PENETRATION OF A WORKPIECE, SAIDFIRST THREAD HAVING A RELATIVELY SMALL INCLUDED ANGLE AND SAID SECONDTHREAD HAVING AN INCLUDED ANGLE SUBSTANTIALLY LARGER THAN SAID FIRSTTHREAD, ALL OF SAID THREADS HAVING ROOTS OF SUBSTANTIALLY THE SAME AXIALEXTENT, AND SAID SHANK INCLUDING A SUBSTANTIALLY POINTED WORK DRILLINGTIP, ALL OF SAID THREADS HAVING A SUBSTANTIALLY UNIFORM ROOT DIAMETERTHROUGHOUT AND SUB-